The present invention relates to a radome and, more specifically, to a radome having a surface that can be configured to filter out one more radio frequency (RF) signals.
A large number of radar systems require a radome to provide environmental protection to radio frequency and other sensors and sources placed behind the aperture. Such radomes are sometimes designed and optimized to have high performance characteristics in that they provide for minimum radio frequency (RF) loss, are ruggedized for environmental protection and are relatively light weight with little regard to low cost. These radomes can be designed for commercial and/or military applications and can be optimized to transmit or reject different frequency bands of the electromagnetic spectrum. In addition, radomes sometimes need to be resistant to and sealed against moisture, chemicals, gases and dust, plus be able to withstand wide temperature ranges and have a required color. It is often needed that designers sacrifice low cost to meet all these other requirements.
High performance radomes require careful selection and understanding of material properties that directly affect radome and antenna or phase array performance. The combination of high performance requirements and a requirement for low cost create a problem where a solution is not intuitively obvious.
Front-end RF filtering is needed in almost every phased array/communication application to limit the sensed or transmitted spectrum. That is, in some cases, a particular frequency may need to be filtered out so that it does not overpower all other frequencies. For example, consider an aircraft passing over a radio station antenna. As is passes over the antenna, both the primary and harmonic frequencies may be so large as to hide other important information in other regions of the spectrum.
Often times the properties of this filter are fixed based on established mission requirements, but a fixed filter will not let an aircraft adapt to changing conditions while in flight. Thus, in the example above, a fixed filter could be applied to block out the radio signal. However, in another location, a different source of interference could be present that is not adequately accounted for by the fixed filter. As such, in these situations, the radar system could be less useful. That is, without a tunable front end filter, the radar system may have several regions where it works less effectively depending on external conditions.
One method of dealing with such large or overpowering signals is to attenuate the entire system, operating with degraded SNR or steering the beam away from the interferer. In all these cases, the system is not operating as intended and will typically sacrifice overall performance all the time to be able to operate through these rare events.